Lead tetraacetate reactions with

R = cyl), eg, with -nitrobenzoyl chloride. Upon reaction with lead tetraacetate, di(hydroperoxyalkyl) peroxides can also be converted to cycHc diperoxides (4). They are also converted to symmetrical or unsymmetrical cycHc triperoxides (5) in the presence of a second ketone and a catalyst, eg, CuSO -HCl (44,119). 

Although some of the oxidative ring closures described above, e.g. reactions with lead tetraacetate (Section 4.03.4.1.2), may actually involve radical intermediates, little use has been made of this reaction type in the synthesis of five-membered rings with two or more heteroatoms. Radical intermediates involved in photochemical transformations are described in Section 4.03.9. Free radical substitutions are described in the various monograph chapters. 

A direct method for introduction of a C-21 acetoxyl group into a 20-keto-pregnane is by reaction with lead tetraacetate at room temperature. Although originally the reaction carried out in hot acetic acid gave low yields, a careful study by Henbest has defined conditions so that yields as high as 86 % can be obtained at room temperature. The preferred solvent is 5 % methanol in benzene, with boron trifluoride etherate as catalyst. With either methanol or benzene, the yield is less than 4%. 

The oxidative cleavage of the central carbon-carbon bond in a vicinal diol 1, by reaction with lead tetraacetate or periodic acid, yields two carbonyl compounds 2 and 3 as products. 

Dicarboxylic acids undergo to-decarboxylation on reaction with lead tetraacetate to give alkenes. This reaction has been of occasional use for the synthesis of strained alkenes. 

Irradiation of the substituted cyclohexadiene resulted in the formation of the Dewar benzene skeleton by a disrotatory ring closure. Reaction with lead tetraacetate (a reaction that is not covered in this book) was used to remove the anhydride group and introduce the final double bond of Dewar benzene. Again, because of the forbidden nature of the conrotatory opening to benzene, Dewar benzene has an appreciable lifetime. At 25°C the half-life for its conversion to benzene is 2 days, and at 90°C its half-life is 30 min. 

Symmetrical divinyllead diacetates can be obtained directly from the corresponding vinylboronic compound through reaction with lead tetraacetate in chloroform at room temperature. Thus, the reaction of (E)-styrylboronic acid 59 with lead tetraacetate in chloroform afforded the bis-(/. )-styryllead diacetate 60 and the reaction of ( )-hex-l-enylboronic acid 61 led to the relatively unstable bis-[fE)-hex-l-enyl]lead diacetate 62 (Equations (54) and (55)). 

The tricyclic peroxide (43) ( triacetylmethane peroxide ) is formed (yield 20%) in an exothermic reaction when 80% sulfuric acid is added to a mixture of triacetylmethane and 40% hydrogen peroxide. The tricyclic structure is proved by the conversion of 42 into 43 on reaction with lead tetraacetate. In agreement with structure 43, the NMR spectrum contains two sharp singlets at t= 8.35 and t = 5.98.44... 

The conversion to primary acetates is carried out in higher yield if the hydroalumination is conducted with only 2 equiv. of the alkene followed by reaction with lead tetraacetate (equation II). ... 

Reactions with lead tetraacetate and iodine are frequently complicated by bifunctional attack, leading to lactols (9) after hydrolysis of intermediate a -iodo-ethers (8). This does not arise in reactions with lead tetraacetate alone (section 5). In general terms, the hypoiodite reaction sequences appear to be of the type depicted in Fig. 48 [34]. 

The subsequent cycMsation of the alkoxy-radical depends upon its ability to attack a suitably placed C-H bond on the -carbon atom. The alternative to cyclisation under homolytic conditions is fragmentation of the alkoxy radical into a carbonyl compound (ii) and an alkyl radical (10), which affords a mixture of stable products by further transformations. Heusler [44] reached similar conclusions from a study of steroid reactions, and has demonstrated a close similarity between thermally and photolytically-induced homolytic reactions with lead tetraacetate in hydrocarbon solvents. 

An improved method for the total synthesis of ISQ alkaloids, such as 91, via a l-azatricyclo[3.2.1.0 ]octane (89) intermediate aziridine and an indoleacetic anhydride (90) has been described by Nagata and Hirai [94,95] (Scheme 10). 3-Cyclohexane-1-methylamine (88) was converted into aziridine 89 by reaction with lead tetraacetate, which was subsequently reacted with 90 to yield 91. 

M. Lj. Mihailovic, A. Stojiljkovic, and V. Andrejevic, Tetrahedron Letters, 461 (1965). For other papers by this Yugoslavian group on Reactions with Lead Tetraacetate, see M. Lj. Mihailovic et ai, Tetrahedron, 21,955 (1966). See also ref. 52. 

The reaction of olefins with lead tetraacetate has not been a useful method in organic synthesis, because reactions such as addition of an oxygen functional group to the double bond, substitution of hydrogen at the allylic position, and C-C bond cleavage can occur to give complex mixtures of products. With some specific alkenes, however, reaction with lead tetraacetate can afford synthetically important compounds cleanly. For instance, reaction of the diacid with 6 equiv. lead tetraacetate in acetonitrile gave the dilactone in excellent yield (Scheme 13.36) [59]. 

Aromatic primary amines react with lead tetraacetate to give symmetrical azo compounds in varying yields, via hydrazo intermediates." " However, in the case of 2,4,6-tri-tert-butylaniline, reaction with lead tetraacetate in benzene at 5°C led to a mixture of three products, the formation of which can be explained by a ligand coupling process. (Scheme 7.2)... 

It is assumed that, in the reaction of arenes with aryllead triacetates, the arylation takes place via the corresponding cationic TC-complexes. In the reaction with lead tetraacetate, an electron transfer-radical cation mechanism was postulated. 1 3 jn agreement with this assumption, 4,6,8-trimethyl-... 

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